Wellbores for the production of hydrocarbon fluid generally are provided with steel casings and/or liners to provide stability to the wellbore wall and to prevent undesired flow of fluid between the wellbore and the surrounding earth formation. A casing generally extends from surface into the wellbore, whereas a liner may extend only a lower portion of the wellbore. However in the present description the terms “casing” and “liner” are used interchangeably and without such intended difference.
In a conventional wellbore, the wellbore is drilled in sections whereby each section is drilled using a drill string that has to be lowered into the wellbore through a previously installed casing. In view thereof the wellbore and the subsequent casing sections decrease in diameter with depth. The production zone of the wellbore therefore has a relatively small diameter in comparison to the upper portion of the wellbore. In view thereof it has been proposed to drill a “mono diameter” wellbore whereby the casing or liner to be installed is radially expanded in the wellbore after lowering to the required depth. Subsequent wellbore sections may therefore be drilled at a diameter larger than in the conventional wellbore. If each casing section is expanded to the same diameter as the previous section, the wellbore diameter may remain substantially constant with depth.
US 2010/0257913 A1 discloses an expansion system whereby an actuator pulls an expansion device through a tubular element. The actuator is anchored in the tubular element by means of an anchor having a resilient anchoring member that is activated by axial compression.
WO 2013/172856 A1 discloses a hydraulic anchoring tool including upper and lower slip systems for use in either cased or open hole wellbores. The tool is activated by hydraulic pressure in a work string.
It is a drawback of the known hydraulic anchoring tool that, when the anchor is to be deactivated for example to displace the anchor in axial direction, there may still be a high fluid pressure in the workstring after releasing the hydraulic pressure at surface. This may result in high contact forces between the slips and the inner surface of a tubular element against which the slips are anchored, and may cause damage to the the inner surface or coating applied to the inner surface.
U.S. Pat. Nos. 4,393,931; 3,677,341; 5,878,818 and 2,765,855 and US patent application US2012/037381 disclose other known anchoring tools that may damage the downhole tubular and/or cannot be released therefrom after deactivation.